Down draft carburetor



March 19, H KlRBY DOWN DRAFT CARBURETOR Original Filed May 31, 1929 4-Sheets-Sheet yen UH March 19, 1935. I c. H. KIRBY Re. 19,503

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DOWN DRAFT CARBURETOR Original Filed May 31, 1929 4 Sheets-Sheet 4 ZJEVEF UH chQTlS I Reissued Mar. 19, 1935- UNITED STATES PATENT' OFFICEDOWN 1mm cmmmn'ron Charles H. Kirby, Flint, Mich., assignor to MarvelOarbureter Company, Flint, Mich., a corporation of Illinois Original No.1,918,974, dated July 18, 1933, Serial No. 367,211, May 31, 1929.

Application for reissue May 29, 1934, Serial No. 728,193

16 Claims.

5 and discharging downwardly therein.

Carburetors of the down 'draft type eliminate a number of troublescommon to the more usual forms of up draft carburetors such as loadingwhen the engine is checked to its idling speed after a spurt. It isaccordingly an object of this invention to provide an improvedcarburetor of the down draft type incorporating a flap type of air valvefor controlling the main air supply, together with a primary air supplyformed as a by-pass around the air valve and having a common choke valvefor both air supplies to render starting a cold engine easier byincreasing the suction acting on the idling fuel supply. Thisarrangement permits making the air supply passages larger than wouldotherwise be the case and permits an increase in the capacity for agiven size over the up draft type. as the mixing chamber may be madeconsiderably larger without developing body loading due to low airvelocities.

It is another object of this invention to provide an improvedaccelerating fuel supply arrangement comprising separate acceleratingpumps incorporated in the low and high speed ,fuel supply conduits andseparately actuated by the throttle and air valve so that theaccelerating charges for the two sets of nozzles can be separatelycontrolled to provide maximum performance at intermediate speed rangeswith a further refinement as to regulation of the accelerating fuelsupply according to the rapidity of opening of the throttle and airvalve.

It is also an object of this invention to provide an improvedaccelerating fuel supply embodying a seasonal regulating means forvarying the effectiveness of the accelerating pump to increase ordecrease the amount of fuel delivered by the pump in accordance with therequirements of the engine under different operatingconditions.

It is still another object of this invention to provide a carburetor ofthe type described embodying features adapted to develop maximumperformance while being comparatively simple to manufacture, assembleand service, with the maximum adjustability for different operatingconditions and requirements.

'Other and further important objects of this invention will be apparentfrom the disclosures in the specification and accompanying draw- 1112s.

The invention (in apreferred form) is illustrated on the drawings andhereinafter more fully described.

n the drawings:

Figure 1 is an elevation of a carburetor embodying the featuresofthis'invention.

Figure 2 is a plan view thereof.

Figure 3 is a section on line III-III of Figure 1.

Figure 4 is a fragmentary detail section of a modified nozzle structure.

Figure 5 is a. section on the line V--V of Figure 3.

Figure 6 is a section on the line VI-VI of Figure 2.

Figure 'l is a section on the line VII-VII of Figure 2.

Figure 8 is a section on the Figure 2.

Figure 9 is a distorted or diagrammatic layout showing the entire pathof fuel travel to the low speed nozzle as separately shown in Figures 3,'1 and 8.

Figure 10 is a similarly diagrammatic showline V IIIVIII of ing of thefuel passages for the high andinter- 5 mediate speed fuel nozzles, thevarious passages shown in Figures 3, 5 and 6' being laid out in a.common plane.

As shown on the drawings: The carburetor as a whole comprises adownwardly discharging mixing chamber 15 in a body member 16, an airvalve 17 therein mounted on a cross shaft 18 to control the majorportion of the air supply over and above the maximum requirements forsatisfactory idling. The entire air supply enters through a passage 19in the body which is controlled by a choke valve 20 of theusual type.The body member 16 forms a separate casting having in addition to themixing chamber 15 and passage 19, a chamber 21 for an air valve dash potlever 22 and link 23 connected to a piston 24 operating in an externallyadjustable sleeve 25 containing a spring 26 urging the piston 24downwardly. From the linkage shown in Figure 3 it will be evident thatthe opening movement of the air valve 17 is resisted by the spring 26 aswell as the damping effect of the closed air chamber 27 formed withinthe sleeve above the piston. The air valve is counterbalanced as shownto compensate for the weight of the piston. By screwing down on thesleeve the initial spring pressure may be increased to increase theresistance of the air valve thus in effect enriching the fuel to airmixture ratio. The body member 16 also contains a. bypass passage 28leading around the closed air valve to a horizontally located primaryventuri 29 discharging into the mixing chamber 15 below the air valve.The outlet or bottom of the mixing chamber connects to a separatejacketed member 30 containing a throttle valve 31 on a throttle shaft32, the passage 33 in the member 30 being given a Venturi form to assistin securing a well balanced mixture of the low speed or-primary supplyand that passing the air valve.

The fuel supply and metering arrangements are located in a separate body34 secured to the side of the body member 16 and comprise separate lowand high speed fuel feeding systems each having individual acceleratingpumps. A fuel chamber 35 has a fuel inlet connection 36 and the usualfloat 37 controlling said inlet.

The low speed fuel supply to the primary venturi 29 comprises adownwardly extending passage 38 opening from the fuel chamber 35 andconnecting to a horizontal ball check chamber 39 containing a ball 40,the chamber 39 having a tapered ball seat so formed as to normally holdthe ball off its seat by its own weight until the back fiow of fuelreaches a velocity sufficient to roll the ball up against its seat whenthe accelerating pump is operated at a predetermined rapidity. From thechamber 39 a passage 41 leads into an accelerating pump chamber 42containing a piston 43 and piston rod 44 linked by a lever 45 to the airvalve shaft 18 so that the piston is moved downwardly during the openingmovement of the air valve and vice versa. The chamber 42 has a reliefpassage 46, leading back to the fuel chamber from above the piston toprevent air binding during the closing movement of the air valve. Thispassage 46 together with the passage 41 are formed in a boss 47connecting the fuel chamber to a nozzle supporting member 48, as bestshown in Figure 7, while the diagrammatic showing'of Figure 9 gives amuch clearer disclosure of the purpose of these connections. As shown inFigure 9 an outlet passage 49 leads from the accelerating pump chamber42 to a chamber 50 in a boss 51 supporting a low speed nozzle 52 whichextends upwardly into the throat of the primary venturi 29. In theactual structure as shown in Figures 7 and 8 the passage 49 branches offfrom the passage 41, part of the fuel discharging through the nozzle 52and part returning to the fuel chamber 35 past the ball 40 unless thisball is seated by the backward rush of fuel when the air valve opens sosuddenly as to close this ball check. The intermediate and high speedfuel supply, which functions upon opening of the air valve 16, is bestshown diagrammatically in Figure 10 as this figure correlates thesections shown in Figures 3, 5 and 6. A passage 53 from the fuel chamberopens into a valve chamber 54, a fiat valve seat 55 being formed aroundthe opening. From this chamber apassage 56 leads to an accelerating pumpchamber 57 and thence through a bushing 58 and a passage 59 to twovertical passages 60 and 61 in the nozzle supporting member 48, thepassage 60 leading to a high speed nozzle tube 62 having a restrictedorifice tip 63 while the passage 61 leads to a lower intermediate speednozzle tube 64 restricted by a tip 65. The two nozzles terminateadjacent the air valve in a position to discharge fuel into the airstream flowing past the valve when the static head as well as thesuction set uppast its tip due to a partial opening of the air valve.

The accelerating pump chamber 57 previously mentioned contains a piston66 having a downwardly extending metering rod 67 entering the bushing 58to restrict the orifice therethrough. This rod is so formed as to nearlyclose the orifice for the first portion of the downward movement of thepiston'and is cut down to a smaller diameter to enlarge the opening forthe later portion of the piston travel. The piston has a piston rod 68engaged by an arm 69 pivoted at 70 and connected by a link 71 to a lever72 on the throttle shaft 32, the linkage being so arranged that anopening movement of the throttle valve forces the piston 66 downwardly.As at the usual driving range it is desired to maintain conditions ofmaximum economy the rod 67 is so calibrated as to restrict the fuelsupply flowing through the bushing 58 while for maximum power at nearlyfull throttle, the restriction is practically eliminated by the reduceddiameter of the rod 67.

The valve chamber 54 contains a disc valve 73- flat valve seat 55 butclose thereto so that the pressure developed by the accelerating pump isadapted to lift the disc against its seat to prevent return of the fuelto the fuel chamber 35. As the accelerating charge supplied to thehigher speed nozzles is not required for proper performance in summerweather a seasonal control adjustment is provided comprising a rod 75projecting through the cover 76 of the fuel chamber 35. This rod isurged downwardly by a spring 77 and its lower end acts to hold the disc73 away from its seat thus rendering the accelerating pump inactive. Theposition of the rod may be adjusted in any convenient manner to controlthe upward or seating movement of the disc 73. As shown the exposed endof the rod carries a lever 78 having V shaped downwardly pointingprojections 79 which drop into corresponding notches in a boss 80 on thecover to form the summer adjustment, while when the lever is turned tocause the projections to ride up on the boss the rod is raised and thedisc is free to rise against its seat, rendering the accelerating pumpfully effective. A series of notches can be provided of varying depthsin the boss to give a series of adjustments between the extremesmentioned.

Figure 4 illustrates an alternative form of nozzle structure whereinintermediate and high speed nozzles 84 are of the air bleed type andhence unrestricted. In this form the vertical passage 81 is providedwith a fuel metering nozzle 82. the passage 81 having an air bleedconnection 83. The passage 81 shown feeds the lower or intermediatenozzle, a similar passage and metering nozzle controlling the feed tothe upper nozzle passages corresponding to 60 in Figure 3.

In the operation of this carburetor closing the choke valve for startingcuts off the entire air supply except for leakage about the choke valve,and hence assures the maximum suction within the carburetor when theengine is turned over so that the fuel drawn from the low speed nozzlewill form a very rich priming mixture that will facilitate firing even avery cold engine.

When the engine is running idle with the choke valve open, the air valveremains closed, the air supply passing through the small primary venturiwhere it is mixed with fuel discharged from the low speed nozzle. Undersuch operating conditions the discharge ends of the two higher speednozzles are not subjected to sufficient suction to lift fuel even to thelevel of the intermediate fuel nozzle.

As the throttle is gradually opened from the idling position theintermediate nozzle begins to supply fuel as the suction in the mixingchamber increases to a point sufficient to swing the air valve partiallytowards its open position. If the throttle movement is slow, the highspeed accelerating pump moves slowly enough to permit the return of mostof the fuel below the pump piston to the fuel chamber past the discvalve '73. On the other hand if the'throttle opening is rapid more fuelwill be injected through the nozzles and less fuel will be returned tothe fuel chamber. A sudden opening of the throttle also results in arapid opening of the air valve, due to the application of a highmanifold suction thereto and the air valve in turn actuates the lowspeed accelerating pump, a rapid motion of which seats the ball checkvalve and causes the accelerating pump to both eject fuel through thelow speed nozzle and to act as a dash pot to slow down the openingmovement of the air valve to prevent fluttering thereof due to unevensuction impulses in the manifold. It is to be noted that this action isa one way one effective only in opposing the rapid opening of the airvalve.

. During the latter part of the throttle opening movement thecorresponding downward movement of the high speed accelerating pump,enlarges the eifective fuel passage in the bushing 58 and thus gives aricher mixture through the two higher speed nozzles thus materiallyincreasing the power of the engine in the range close to full openthrottle, while maintaining a more economical fuel and air mixture ratiofor the more common operating conditions of a partly open throttle.

It will thus be seen that I have provided an improved downdraftcarburetor embodying features of a variable accelerating charge controlamendable both to the seasonal and operating variations in the amount ofaccelerating fuel required to maintain satisfactory acceleration withoutloading, together with a lean and economical mixture ratio for normaloperating conditions while having in reserve a richer mixture ratio todevelop maximum power at full throttle. Further, starting a cold engineis made easier by cutting off the primary air supply as well as the mainair supply by a common choke valve.

I am aware that numerous details of construction may be varied through awide range without departing from the principles of this invention, andI therefore do not purpose limiting the patent granted, otherwise thannecessitated by the prior art.

I claim as my invention:

1. In a carburetor, a downwardly discharging mixing chamber, a flapvalve controlling the admission of themajor quantity of air thereto, aventuri controlling the admission of primary air thereto, a common airinlet for both air supplies, a choke valve controlling said air inlet, afuel supply chamber, separate fuel supply conduits discharging into theseparate air supplies entering said mixing chamber and acceleratingpumps associated with each supply conduit.

2. In a carburetor, a downwardly discharging mixing chamber, a flapvalve controlling the admission of the major quantity of air thereto, aventuri controlling the admission of primary air thereto, a common airinlet for both air supplies, a choke valve controlling said 'air inlet,a fuel supply chamber, separate fuel supply conduits discharging intothe separate air supplies entering said mixing chamber, acceleratingpumps associated with each supply conduit and means for regulating thedelivery of said pumps.

3. In a carburetor of the down draft type in combination with a fuelsupply chamber separate high and low speed fuel supply conduits'andnczzles, accelerating pumps associated with each fuel conduit, means forvarying the delivery from one of said accelerating pumps and meansassociated with each pump adapted to render said pumps inoperative belowa predetermined rapidity of action.

4. In a down draft carburetor including a mixing chamber, a fuelchamber, a throttle valve and an air inlet passage, a primary venturidrawing air from said air-inlet passage and discharging into said mixingchamber, an air valve controlling the passage of the main air supplyfrom said air inlet to said mixing chamber, a fuel supply conduit andnozzle discharging into said primary venturi, a second fuel supplyconduit and nozzles discharging into said main air supply adjacent theair valve, an accelerating pump in one of said fuel supply conduits andlinkage connecting said pump to the throttle to be actuated thereby.

5. In a down draft carburetor including a mixingchamber, a fuel chamber,a throttle valve, and an air inlet passage, an air valve controlling thesupply of air from said air inlet to said mixing chamber, a bypass airpassage around said air valve, said passage including a primary venturi,a fuel supply conduit discharging into said venturi, a second fuelsupply conduit and nozzles discharging into said main air supplyadjacent the air valve, an accelerating pump in said second fuel supplyconduit and linkage connecting said pump to the throttleto be actuatedthereby.

6. In a down draft carburetor including a. mixing chamber, a. fuelchamber, a throttle valve and an air inlet passage, an air valvecontrolling the supply of air from said air inlet to said mix ingchamber, a bypass air passage around said air valve said passageincluding a primary venturi, a fuel supply conduit discharging into saidventuri, a second fuel supply conduit and nozzles discharging into saidmain air supply adjacent the air valve, an accelerating pump in saidsecond fuel supply conduit, linkage connecting said pump to the throttleto be actuated thereby, and means actuated by said pump adapted to meterthe fuel in said second conduit in accordance with the throttle opening.

7. In a down draft carburetor including a mixing chamber, a fuelchamber, a throttle valve and an air inlet passage, an air valvecontrolling the' supply of air from said air inlet to said mixingchamber, a bypass air passage around said air valve said passageincluding a primary venturi, a fuel supply conduit discharging into saidventuri, a second fuel supply conduit and nozzles discharging into saidmain air supply adjacent the air valve, an accelerating pump in saidsecond fuel supply conduit, linkage connecting said pump to the throttleto be actuated thereby and means in said second fuel supply conduitadapted to adjustably vary the effectiveness of the pump.

8. In a down draft carburetor including a mixture chamber, a fuelchamber, a throttle valve and an air inlet passage, an air valvecontrolling the supply of air from said air inlet to said mixingchamber, a bypass air passage around said air valve said passageincluding a primary ventun, a fuel supply conduit discharging into saidventuri, a second fuel supply conduit and nozzles discharging into saidmain'air supply adjacent the air valve, an accelerating pump in saidsecond fuel supply conduit, linkage connecting said pump to the throttleto .be actuated thereby, means actuated by said pump adapted to meterthe fuel in said second conduit in accordance with the throttle openingand means in said second fuel supply conduit adapted to adjustably varytheeffectiveness of the pump.

9. In a down draft carburetor including a downwardly discharging mixingchamber, a fuel chamber, a throttle valve and an air inlet passage, anair valve controlling the supply of air from said air inlet to saidmixing chamber, means for adjustably retarding the opening movement ofsaid air valve, a bypass air passage around said air valve said passageincluding a primary venturi discharging into said mixing chamber, a fuelsupply conduit discharging into said venturi,

' an accelerating pump in series with said conduit,

and linkage connecting said pump and air valve.

10. In a down draft carburetor including a mixing chamber, a fuelchamber, a throttle valve and an air inlet passage, an air valvecontrolling the supply of air from said air inlet to said mixingchamber, means for adjustably retarding the opening movement of said airvalve, a bypass air passage around said air valve, said passageincluding a primary venturi, a fuel supply conduit discharging into saidventuri, an accelerating pump in series with said conduit and linkageconnecting said pump and air valve, and means in said fuel supply forrendering said accelerating pump ineffective below a predeterminedrapidity of movement.

11. In a carburetor a downwardly discharging mixing chamber, an airinlet passage extending upwardly from said chamber, a fiap type,suction-operated, air valve interposed between the mixing chamber andthe inlet passage controlling the flow of air from the passage to thechamber, a bypass air passage for primary air leading from the inletpassage and terminating in a horizontally disposed venturi discharginginto the mixing chamber below the air valve, a low-speed nozzledischarging into said venturi, an intermediate and a high speed nozzlehorizontally disposed and discharging into the inlet passage immediatelyabove the air valve, the intermediate speed nozzle being spacedvertically below the high speed nozzle and discharging when said airvalve is partially open, said high speed nozzle discharging when saidvalve is opened to a greater extent, and fuel supply passages for saidnozzles.

12. In a carburetor a downwardly discharging mixing chamber, an airinlet passage extending upwardly from said chamber substantially invertical alinement therewith, an air valve operated by suction andcontrolling the flow of air directly from said inlet passage to saidchamber, a bypass air passage for bypassing primary air around saidvalve leading from the inlet passage above said valve and terminating ina horizontally disposed venturi discharging into the mixing chamberbelow the air valve, a primary fuel supply discharging into saidventuri, and a secondary fuel supply discharging into the inlet passageimmediately above the air valve and controlled thereby to discharge whenthe suction is sufiicient to open the air valve.

13. In a carburetor a downwardly discharging mixing chamber, an airinlet passage extending upwardly from said chamber, a suction operatedair valve controlling the supply of air from the inlet passage to themixing chamber, a bypass air passage for bypassing primary air aroundsaid valve leading from the inlet passage above said valve andterminating in a venturi discharging into the mixing chamber below theair valve, a low speed fuel supply conduit discharging into the venturi,an intermediate speed nozzle anda. high speed nozzle vertically spacedand discharging into the inlet passage adjacent the air valve, and afuel supply conduit for each of said nozzles.

14. In a carburetor a downwardly discharging mixing chamber, an airinlet passage extending upwardly from said chamber, a suction operatedair valve controlling the flow of air directly from the inlet passage tothe chamber, a bypass air passage for bypassing primary air around saidvalve leading from the inlet passage above said valve and terminating ina venturi discharging into the mixing chamber below the air valve, 2.primary fuel supply discharging into said venturi, a vertical ductterminating in a nozzle discharging into the inlet passage immediatelyabove the air valve and controlled thereby, a metering nozzle in saidduct connected to a fuel supply, and an air bleed opening for said ductforming with the metering nozzle an emulsion of fuel and air.

15. In a carburetor a downwardly discharging mixing chamber, an airinlet passage extending upwardly from said chamber, an air valveoperated by suction and controlling the flow of air directly from saidinlet passage to said cham ber, a bypass air passage for bypassingprimary air around said valve leading from the inlet passage above saidvalve and terminating in a venturidischarging into the mixing chamberbelow the air valve, a primary fuel supply discharging into saidventuri, and means forming an emulsion of fuel and air discharging intothe inlet passage immediately above the air valve and controlled inaccordance with the extent of opening thereof.

16. In a carburetor a downwardly discharging mixing chamber, an airinlet passage extending upwardly from said chamber, an air valve peratedby suction and controlling the flow of air directly from said inletpassage to said chamber, an air passage for bypassing primary air aroundsaid valve leading from the inlet passage above said air valve andterminating in a venturi discharging into the mixing chamber below theair valve, said by-pass air passage having its end leading from saidinlet passage projecting into said inlet passage beyond the wall thereofin a substantially upward direction, a fuel supply chamber, and separatefuel supply means discharging respectively into the venturi and into theinlet passage above the air valve, the discharge into the inlet passagebeing controlled by the extent of opening of said air valve.

CHARLES H. KIRBY.

